1. Field of the Invention
The present invention relates to a control mechanism for an optical system, and, in particular, to a control mechanism for an optical system in an image-forming device such as a copying machine and the like.
2. Description of the Prior Art
Scanning by an optical system in an image forming device is generally controlled by the amount and the direction of an electric current supplied in the DC mode. To prevent blurring of the image and to ensure the specifications are met, both a forward and a return scan and negative feedback control using PLL are used.
In the conventional technology mentioned above, for PLL control, a specific scanning velocity is maintained along the scan, and when the forward or the return scan is commenced a transient current flows so that an overshoot or undershoot is produced in the motor speed waveform.
FIG. 1 is a view showing the circumstances of the development of such a problem point.
A direction signal F indicates a forward scan and R indicates a return scan. A start signal ST is OFF only during times t.sub.1 to t.sub.2 and t.sub.4 to t.sub.5.
At the initial period of the forward and return scans, it can be seen that a large change (overshoot, undershoot) occurs in the motor speed.
In the return scan, if the return time is maintained within a set specification there is no problem, but because a document is copied during the forward scan, there is concern that a blurring of the image at the leading edge of the document will be produced.